Field of the Invention
The present invention relates to a charged particle beam writing apparatus and a buffer memory data storage method. More specifically, for example, the present invention relates to a writing apparatus that performs data processing for each processing region by inputting writing data into a buffer memory, and a method therefor.
Description of Related Art
The lithography technique that advances miniaturization of semiconductor devices is extremely important as being a unique process whereby patterns are formed in semiconductor manufacturing. In recent years, with high integration of LSI, the line width (critical dimension) required for semiconductor device circuits is decreasing year by year. For forming a desired circuit pattern on such semiconductor devices, a master or “original” pattern (also called a mask or a reticle) of high accuracy is needed. Thus, the electron beam (EB) writing technique, which intrinsically has excellent resolution, is used for producing such a high-precision master pattern.
FIG. 9 is a conceptual diagram for explaining operations of a variable shaped electron beam writing or “drawing” apparatus. As shown in the figure, the variable shaped electron beam writing apparatus operates as described below. A first aperture 410 has a quadrangular opening 411 for shaping an electron beam 330. A second aperture 420 has a variable-shape opening 421 for shaping the electron beam 330 having passed through the opening 411 of the first aperture 410 into a desired quadrangular shape. The electron beam 330 emitted from a charged particle source 430 and having passed through the opening 411 is deflected by a deflector to pass through a part of the variable-shape opening 421 of the second aperture 420, and thereby to irradiate a target object or “sample” 340 placed on a stage which continuously moves in one predetermined direction (e.g., the x direction) during the writing. In other words, a quadrangular shape that can pass through both the opening 411 and the variable-shape opening 421 is used for pattern writing in a writing region of the target object 340 on the stage continuously moving in the x direction. This method of forming a given shape by letting beams pass through both the opening 411 of the first aperture 410 and the variable-shape opening 421 of the second aperture 420 is referred to as a variable shaped beam (VSB) system.
When reading writing data in which positions, shapes, etc. of patterns to be written are defined into a memory in a writing apparatus, generally, the data is sorted and stored in a memory region (memory space) by a commercial operating system (OS) that controls the control computer. Then, in the processing side wherein data processing is performed, data is read from the memory and conversion of the data is performed to generate data required for writing processing. In the writing apparatus, in parallel with an actual writing operation irradiating electron beams, data processing for a next writing processing region is executed in real time. In the system side, when the amount of memory used exceeds a specified amount, data not being used at the time is deleted from the memory by a garbage collection function performed by the OS. Then, next data is sequentially stored in an empty region. In recent years, the number of patterns written is increased, and their shapes are various. If data of such patterns is read into the memory by the OS control, fragmentation may occur in the memory. Furthermore, if the memory capacity becomes insufficient, the OS performs a swap-out by using the hard disk etc.
As described above, when memory control is performed by the OS, fragmentation or swap-out is performed in the memory. This causes a problem that when data processing is performed in the processing side, the data read-out time becomes long and the data processing speed of writing data is deceased. Accordingly, a problem occurs that data processing itself may be stopped in some cases, thereby causing a stop of writing processing.